(a) Field of the Invention
The present invention relates to an electronic ballast capable of linear and stepless light regulation, more particularly to an electronic ballast in which the modulation of a variable resistor is utilized to charge a fifth capacitor, the charging speed being contrary to the size of the modulated resistance value of the variable resistor. When the voltage of the fifth capacitor has reached a bending voltage of connection of a bilateral thyristor, the bending point slows down with the augmentation of the resistance. On the contrary, the smaller the resistance, the earlier the bending point, causing the bilateral thyristor become connected and output a trigger pulse, then the second transistor is connected, so that a positive pulse of a sinusoidal wave that passes a limiting inductor, two cathode coils of the fluorescent lamp, the first mutual inductor and the second transistor to be chopped. The size of the chopped pulse is determined according to the size of the resistance value to control the luminosity of the fluorescent lamp. The positive pulse of the chopped pulse is used to generate a counter electromotive force with respect to second and third mutual inductors when it passes through the first mutual inductor to chop the second transistor and connect the first transistor. The positive pulse passes through the first transistor and passes the first mutual inductor in a reverse direction, inducing a counter electromotive force in a reverse direction with respect to the second and third mutual inductors so that the first transistor is chopped and the second transistor is connected at the same time. The first transistor and the second transistor are alternately connected and cut off to form semi-symmetrical resonance to allow linear light regulation of the fluorescent lamp to maintain the required luminosity under modulation, thereby achieving no flashing during light regulation and an increased light regulation range under no dissipation.
(b) Description of the Prior Art
A conventional electronic ballast generally utilizes the size of the voltage to control the luminosity of the fluorescent lamp. However, there are at least the following drawbacks with the conventional ballast:
a) having an alternating resonance of 120 Hz.; PA1 b) incapable of linear light regulation; PA1 c) poor efficiency PA1 d) smaller light regulation range, about below 50%; and PA1 e) flashing during light regulation.